pm why

Overview

The pm why command shows why a package is installed in your project by displaying the dependency chain that requires it.

This command is not supported for npm. It works with pnpm and bun only.

Syntax

pm why <package> [...args]

Arguments

string

required

The package name to investigate

string[]

Additional arguments passed to the underlying package manager

Examples

Check Why Package is Installed

pm why lodash

Output

Running: pnpm why lodash

dependencies:
lodash 4.17.21
├── my-app
└─┬ some-library
  └── lodash@^4.17.0

Check Transitive Dependency

pm why typescript

Output

Running: pnpm why typescript

devDependencies:
typescript 5.0.0
├── my-app
├─┬ @typescript-eslint/parser
│ └── typescript@>=4.2.0
└─┬ vite
  └── typescript@^5.0.0

Check Deep Dependency

pm why react

Output

Running: pnpm why react

dependencies:
react 18.2.0
├── my-app
├── react-dom → react@^18.2.0
└─┬ @radix-ui/react-dialog
  └── react@^16.8 || ^17.0 || ^18.0

Use Cases

Debug Unexpected Package

Find out why an unexpected package is installed:

pm why some-random-package

Understand Duplicates

Check why multiple versions exist:

pm why react
# Shows all dependency paths requiring react

Audit Dependencies

Investigate security vulnerabilities:

pm why vulnerable-package
# Shows which packages depend on it

Plan Upgrades

Understand dependencies before upgrading:

pm why typescript
# Check what requires specific version

How It Works

From src/commands/why.ts:10-22:

export const whyCmd = cli.Command.make('why', { args: argsArg }, (args) =>
  Effect.gen(function* () {
    const pm = yield* PackageManagerService;
    if (pm.name === 'npm') {
      yield* Console.error('why is not supported for npm');
      return;
    }
    const passthrough = Array.from(args.args);
    const cmd = ShellCommand.make(pm.name, 'why', ...passthrough);
    yield* Console.log(`Running: ${pm.name} why ${passthrough.join(' ')}`);
    yield* runShellCommand(cmd);
  }).pipe(Effect.provide(PackageManagerLayer)),
);

The command:

Detects your package manager
Checks if it’s npm (not supported)
Passes arguments to pnpm why or bun why
Displays the dependency tree

Package Manager Support

Package Manager	Supported	Command
pnpm	✅ Yes	`pnpm why <package>`
bun	✅ Yes	`bun why <package>`
npm	❌ No	Not available

npm users can use npm ls <package> as an alternative, though it provides different output format.

Alternative for npm

If you’re using npm:

npm ls lodash

This shows where the package is used, but with different formatting.

Understanding Output

The output typically shows:

Package version - The installed version
Dependency type - Whether it’s in dependencies, devDependencies, etc.
Dependency chain - The tree of packages that require it
Version ranges - The semver ranges that satisfied the requirement

Example Output Explained

pm why react

dependencies:               # Found in dependencies
react 18.2.0               # Installed version
├── my-app                 # Direct dependency
├── react-dom → react@^18  # Via react-dom (requires ^18)
└─┬ ui-library             # Via ui-library
  └── react@^18.0.0       # Which requires ^18.0.0

This tells you:

React 18.2.0 is installed
It’s a direct dependency of your app
react-dom requires react ^18
ui-library also requires react ^18.0.0

Common Scenarios

Find Dependency Source

pm why @types/node
# Shows which packages need Node.js types

Debug Version Conflicts

pm why react
# If multiple versions exist, shows all paths

Identify Bloat

pm why large-package
# Check if it's really needed

Security Audit

pm why vulnerable-package
# Find all dependents before removing

Workflow Examples

Remove Unused Dependency

Check Usage

pm why lodash

If No Direct Use

If it’s only a transitive dependency, consider alternatives

If Direct Dependency

Remove safely:

pm remove lodash

Investigate Duplicate

Check Why Installed

pm why react

Review Version Ranges

Check if dependencies can use the same version

Update Dependencies

Align versions to remove duplicates:

pm up react

pm ls - List installed dependencies
pm remove - Remove dependencies
pm up - Update dependencies

Get Started

Core Concepts

Commands

Guides

Overview

Syntax

Arguments

Examples

Check Why Package is Installed

Check Transitive Dependency

Check Deep Dependency

Use Cases

Debug Unexpected Package

Understand Duplicates

Audit Dependencies

Plan Upgrades

How It Works

Package Manager Support

Alternative for npm

Understanding Output

Example Output Explained

Common Scenarios

Find Dependency Source

Debug Version Conflicts

Identify Bloat

Security Audit

Workflow Examples

Remove Unused Dependency

Investigate Duplicate

​Overview

​Syntax

​Arguments

​Examples

​Check Why Package is Installed

​Check Transitive Dependency

​Check Deep Dependency

​Use Cases

​Debug Unexpected Package

​Understand Duplicates

​Audit Dependencies

​Plan Upgrades

​How It Works

​Package Manager Support

​Alternative for npm

​Understanding Output

​Example Output Explained

​Common Scenarios

​Find Dependency Source

​Debug Version Conflicts

​Identify Bloat

​Security Audit

​Workflow Examples

​Remove Unused Dependency

​Investigate Duplicate

​Related Commands

Overview

Syntax

Arguments

Examples

Check Why Package is Installed

Check Transitive Dependency

Check Deep Dependency

Use Cases

Debug Unexpected Package

Understand Duplicates

Audit Dependencies

Plan Upgrades

How It Works

Package Manager Support

Alternative for npm

Understanding Output

Example Output Explained

Common Scenarios

Find Dependency Source

Debug Version Conflicts

Identify Bloat

Security Audit

Workflow Examples

Remove Unused Dependency

Investigate Duplicate

Related Commands